The present invention relates to a filter condition sensor and indicator, and more particularly, to a filter condition sensor and indicator that responds to the presence of a predetermined collection of material in a filter that is operatively positioned in an output air flow path which may include a multi-speed fan.
In a product such as a humidifier, vacuum cleaner or other product containing a filter, it is desirable to know when the filter is clogged since this can adversely affect performance. Typically, a clogged filter is one where the air pressure drop across the filter increases.
The prior art has suggested various ways in which a clogged filter can be indicated to a user. U.S. Pat. No. 4,050,291 discloses heated thermistors used in a bridge circuit with a filter sensor and indicator device; U.S. Pat. No. 4,040,042 teaches the use of a current sensing resistor in a blower energizing circuit; and U.S. Pat. No. 4,240,072 discloses an energy sensor in the form of a closed loop flux conducting circuit. All of these prior art techniques have proved to be useful for certain applications.
Sensing the condition of a filter and providing a visual indication of the filter to the user becomes more complicated when a multi-speed fan is used in a product such as those identified above. When the fan speed in changed, the velocity of air through the filter is also changed, and this may cause the indicator to "trip" when the filter is not clogged or fail to indicate a clogged filter.
The present invention has been constructed specifically to overcome the aforementioned problems in a new and improved construction not previously taught or suggested by the prior art.